fix(Progress): clear stale segment values when flipping to indeterminate

[sridhar-3009]

Fixes #814

Root cause

EmProgress.vue passes :model-value="indeterminate ? undefined : model" to Progress.Root. When indeterminate flips to true after a value was already committed, ProgressRoot's internal computed collapses to [], and useProxyModel calls context.apply([]).

createProgress.apply() only wrote incoming values to segments at matching array indices:

for (const [index, element] of clamped.entries()) {
  const ticket = segments.value[index]
  if (!ticket || !isRef(ticket.value) || isReadonly(ticket.value)) continue
  ticket.value.value = element!
}

clamped.entries() is empty when incoming is [], so the loop body never runs — any already-registered segment keeps its old value. isIndeterminate derives from segment values (> 0 means determinate), so it stayed false, and ProgressRoot kept emitting data-state="determinate" and the stale aria-valuenow/aria-valuetext even while Emerald's CSS sweep animation was visibly running — a real accessibility bug (AT reports a fixed value while the bar visually reads as busy/indeterminate).

Fix

apply() now iterates over every registered segment instead of only the incoming array, so a segment with no corresponding entry resets to min:

for (const [index, ticket] of segments.value.entries()) {
  if (!isRef(ticket.value) || isReadonly(ticket.value)) continue
  ticket.value.value = clamped[index] ?? min
}

Since apply() is always called with the full desired model state (see useProxyModel's reconcile), this is the correct general semantic — not specific to the indeterminate case — and doesn't affect any of the existing apply tests (single segment, multi-segment, clamping, pending-registration).

Also fixed the smaller item the issue flagged: the stale comment in EmProgress.vue claiming ProgressRoot always emits aria-labelledby — it's gated on hasLabel (ProgressRoot.vue:144).

Test plan

• Reproduced against the pre-fix code first: added a v-model test that commits a value, then transitions to undefined via wrapper.setProps — failed on main (total stayed 60 instead of resetting to 0), passes with the fix
• pnpm vitest run --project v0:unit → 4700 passed, 1 skipped (no change from baseline)
• pnpm --filter=@vuetify/v0 typecheck and pnpm --filter=@paper/emerald typecheck clean
• pnpm eslint clean on changed files
• Added a changeset (patch bump for @vuetify/v0 and @paper/emerald)